Leather manufacture



' perature resistance.

Patented Apr. 13, 1943 UNITED STATE LEATHER MANUFACTURE I William Orville Dawson, Stamford, Conn, assignor to American Cyanamid Company, New York, N. Y., a corporationof Maine N'o Drawing. Application July 25, 1942,

Serial No. 452,322

I 12 Claims. This invention relates to a new and improved method of preparing leather and more speciflcally to the conversion of untanned hides and skins into leather with methylol melamines in conjunction with another tanning agent. r

In my co-pending application Leather manufacture, filed July 25, 1942, Ser. No. 452,323, it

is disclosed that untanned hides and skins may be converted into uniform pure white, full, plump suede or grain leather by treatment with aqueous dispersions of water-soluble methylol melamlnes. I have now discovered, and this discoveryconstitutes one of the principal features of the present invention, that hides or. skins tanned or partially tanned with methylol melamines may be treated with other tanning agents to particularly good advantage producing results not heretofore thought possible by combinations of conventional tanning reagents or from any particular tanning agent used by itself.

I have found, for example; that a preliminary treatment of an untanned skin with methylol melamine may be followed by treatment with conventional vegetable tanning extracts such as sulflted quebracho extract and the tannage com-' pleted in a matter of hours rather than days as when using the vegetable extract alone. For some reason not yet determined the .hides' and skins pre-treated with methylol melamine allow a faster, but thorough, penetration with tanning extracts and the tanning liquor is exhausted of its tannin in a few hours yielding a piece of leather well tanned and completely struck through. The tanned skins are full, plump and tight grained and have an unusually high'tem- When the leather is torn long, distinct, well-separated fibers are found to predominate.

When using the methylol melamine treatment in conjunction with conventional metal tanning agents a number of unexpected and unsual results are also found. For example, it is commonly known in the art that alum tannages are generally very poor, yielding leathers of poor heat and water resistance.

The alum appears to be poorly fixed in the leather and easily hydrolyzes and washes out thus undoing any tanning effect imparted to the leather. I have found that a pre-treatment of the untanned skin with methylol melamine, as will be particularly described hereinafter, makes it possible to complete the tanning operation with conventional alum type tanning materials to produce a full white leather of good opacity and of good heat and water'resistance. The tanned skins are plump and full and the alum appears, to be. more permanently fixed in the leather;

. .I have also found that pre-treatment of the untanned hides with methylol melamine as described herein makes it possible to secure a very good tannage with iron salts. As is known, iron tannages give fiat, empty, hard leathers which withstand water poorly and which are difllcult to fatliquor. However, my process makes it possible to employ iron salts to produce leathers of a uniform, light yellow color which are full, plump and have exceptionally good' heat resistance. l

As in the case of the vegetable tanning,.it.is not possible to definitely state why the preliminary treatment with methylol melamine makes it possible to secure a satisfactory tannage with various metal tanning agents. Methylol melamine may be fixed in the leather by a number of hypothetically possible chemical reactions with the leather or hydrolysis products of the leather or it may be simply present in a polymerized form. However, it definitely appears to bind the metal salts in the leather preventing them from being hydrolyzed and washed out. Accordingly, one of the principal advantages of my invention is that it makes possible the successful use of metal tanning salts which have heretofore been considered undesirable because of the ease with which they are washed out of the leather.'

My improved tanning method is also particularly advantageous when used in conjunction with such well-known tanning agents as the chrome salts which normally give well tanned leathers of good heat resistance.v I have found I that a preliminary treatment of the untanned hides'with methylol melamine makes it possible to use a considerably smaller amount of the chrome tan and at the same time secure a leather of superior characteristics. For example, leathers prepared by my treatment as herein described are in general much whiter and fuller than those leathers preparedwith straight chrome tanning agents and possess excellent light-resistance.

It will be seen therefore that among the objects of my invention are to provide a method,

of tanning leather which produces a leather of better color, heat resistance, stability, fullness,.

plumpness; better grain and other desirable characteristics in a shorter period of time with.

cheaper and more readily available tanning agents. Other objects of my invention will be apparent from whathas been said'and from what will appear hereinafter.

In carrying out my improved method for tanment in other conventional the tannery.

ning leather I may treatall types, and kinds of untanned fish, bird, reptile or animal skins in their bated, drenched or pickled condition with an aqueous dispersion of a methylol melamine and with another tanning agent, which may be a vegetable tan such as chestnut, quebracho or hemlock or a water-soluble tanning metal salt such asa sulfate of iron, chromium or aluminum.

Usually the skins are preferably first impregnated with the methylol melamine dispersion and the vegetable or mineral tanning agent is then applied but in some cases, notably in the'applica-' tion of partially basic chromic sulfate, the methylol melamine and the other tanning agent may be applied simultaneously. Even in this latter case it is probable that atleast a substantial part of the methylol melamine'is taken up by the skin in advance oi the other tanning agents, but it should be understood that the invention in its.

broader spects is not limited by the exact method of application. r

'I he methylol melamlnes'which I employ in my tion for an excessive length or time should be avoided since polymerization of the compound readily occurs and the more highly polymerized methylol melamines are water-insoluble. Also, sinceskins are ordinarily treated in the preliminary steps of the tanning process with large quantities of salt, it is desirable that the methylol melamine'be water soluble in the presence of salt. Since aqueous dispersions of the higher polymers of methylol melamine are precipitated by salt the methylol melamines employed in my process should for this reason also be prepared by methods which avoid excessive and prolonged heating during their preparation.

Preparation of a methylol melamine suitable for use in my new process may be accomplished by boiling one mol of melamine with about 3.5

mols of aqueous 30% formaldehyde having a pH of 9.0 for about 20 minutes followed by cooling, separating and drying the resulting crystals. These methylol melamine crystals may be readily dispersed in hot water. If desired, a solution of methylol melamine directly usable as a :tanning liquormay be prepared by heating the melamine. and formaldehyde and omitting the step of separating the product from its mother liquor;

As has previously been stated, I prefer to treat the untanned skin with an aqueous dispersion containing 1-10% of methylol melamine until the skin is at least partially tanned before introducing the second tanning agent into the process.

skins it will be found that some tanning occurs within the first hour of the treatment. The

' Since the methylol melamine acts rapidly on the f amine dispersion or by drumming or by treatequipment found in Whenthe skins have been penetrated by'the methylol melamine to the desired degree, which may be any time up to about 24 hours depending upon the type of skin being'treated, the second tanning agent is added atonce or in several feeds as desired. The tanning operation is then imrequired since this too depends. to a great extent upon the particular use to which the leather is to be employed and also the character of the tanning reagent. However, as stated before, the:

preliminary treatment withmethylol melamine enables the tanner to obtain the same degree of tannage with very materially reduced quantities of the tanning agent. 7 a

My invention will now be described in greater detail by means of the following examples. It should be understood that these are given pr marily by way of illustratlon'and are'not' intended to be in limitation of the invention as 'delined by the appended claims.v In these examples the parts are by weight, unless otherwise stated, based on the drained weight of the pickled skins.

- Example 1 parts by weight of pickled calfskins were drummed for-15 minutes at 70 F.-with 60 partsof water and 10 parts of salt. 5 parts of trimethylol' melamine dissolved in 40 parts of water were added at 15 minute intervals tothe drum in 5 separate portions. Following the addition of the final portion of trimethylol melamine the drumming was continued for another hour-at tempera tures not in. excess of 100 F. The solution was then adjusted to a pH range of 3.3-3.7 with sul-' furic acid and the drumming continued for 30 minutes. At this point the liquor had a pilot 3.5 and a sample of the stock easily withstood the action of water at F. Chromic .sultate'in amounts equivalent to 0.75 part chromic oxide (CrrOa) and having a basicity of 33% Schorlemmer was added to the drum in 3 feeds 10 minutes apart and the drumming continued for one hour a after the last addition of the chrome. .At this.

time the liquor had a pH between 3.2 and 3.5 and the tanned stock was able to withstand a shrink .temperature of F. The tanning operation was then completed bywashing, neutralizing, dyeing and fatliquoring in the usual chrome-tanned leathenf Similar results can be obtained by first drumming the methylol melamine-pretreated skins in a chromic acid liquor containing about 1% of.

chromic. acid on the weight of the skins and then sodium thiosulfate i dipping the chromed skins in a liquor in the usual manner.

a pickled goatskin and pickled calfskin weighing 2720 g. were drummed for 15 minutes in 1090 g. of a 15% NaCl solution. 163 g. '(dry weight) of trirnethylol melamine dissolved in 815 g. water was added to the drum and the skins drummed for one hour at a pH of 4.2. Thereupon 425g. of a 20% solution of H2804 was added and the drumming continued for. 3 hours at a pH of 3.8. A 50% basic (Schorlemmer) solution of aluminum sulfat prepared from 272 g. of Alz(SO4)a and 65 s. of NMCO: was then added to the drum andthe skins drummed for 2 hours" longer. The skins were allowed to lie in the drum overnight and the following day were neutralized to a pH of 6.0 using 81.5 g. of soda ash and 54.5 g.

manner on full 1 Example 3 A limed side was split to 12 oz. and divided into two portions, washed minutes at 70 F.. drained, and washed to 90 F. The skin was then for 15 minutes.

Example 4 A pickled top grain side weighing 2040 g. was drummed with 1455 g. of water and 104 g. NaCl 104 g. of trimethylol melamine dissolved in 520 g. of water was added in one feed and the skin drummed 16 hours at which time the liquor had apH of 3.8 and the skin a shrinking temperature of 145 F. A solution prepared'by dissolving 200 g. of Fe2(SO4)a in 200 cc. water with heating was mixed with a solution prepared by dissolving 30 g. of citric acid in 100 cc. water followed by neutralization to a phenolphthalein end-point with NaOH. The mixed solutions-were added to the drum in amounts such that there was present an equivabated with 1% of a commercial enzyme bate in a short liquor. The skins were drummed minutes, washed 15 minutes at F. and drained. One piece of the skin was left in the bated condition and the other was pickled in 200% water, 10% NaCl and 2% H2504 for one hour at a pH of approximately 1.9. I

The pickled skin which has weighed 2950 g. in the limed condition was placed in a drum with of its weight of water and 5% NaCl'and drummed for 15 minutes. 5% (based on the limed weight of the skins) of trimethylol melamine ln 25% of water was added to the drum and the skins drummed for 18 hours at which time the liquor had a pH of 3.7. Disodium phosphate, 295g, was then added and the skins drummed for one hour after which they were washed in cold water for 15 minutes. After washing, the skins had an average shrink temperature of 147 F., a pH of 4.7 on the grain and a pH of 4.0 inside. The skins were then drained and added to of a 3% NaCl solution and drummed for 10 minutes. Tannin (sulfited quebracho) in the amount of 7% based on the limed weight of the skin was then added and the skins drummed for one hour at which time the liquor was almost exhausted. Another 7% of tannin was then added and the drumming continued for another hour.

} An additional 7% tannin was added and the drumming continued for one hour more at which time the skins were completely struck through. The skins were then slicked out, oiled off, and dried in acool dark room.

The sample of bated skin which had weighed 2950 g. out of the lime was placed in a, drum with 70% water containing 5% salt and drummed for 15 minutes. 5% trimethyloi melamine in 25% water was added in one feed and the skins drummed for 45 minutes at which time the liquor had a pH of 8.2. One-half percent of diluted H2804 was then added and the drumming continued for another hour at which time the pH of the solution was 5.2. Dilute H2804 was added to bring the pH down to 3.9. The drumming was then continued for about 18 hours at which time the liquor had a pH of 4.0 and the skins had a shrink temperature of 165 F. One percent of disodium phosphate was added and the skins drummed for one hour at which time they had a shrink resistance of 174 F. They were then washed in cold water for 15 minutes, the liquor was drained from the skin and the skin tanned with quebracho extract, slicked out, oiled of! and dried exactly as described in the case of the pickled skin described in the preceding paragraph. Both pieces of leather were full, plump, tight-grained and well tanned. Upon tearing they showed excellent fiber strength.

.lent of 10% Fe-MSOO: based on the weight of feeds 10 minutes apart and the drumming continued for 30 minutes at which time the liquor .had a pH of 4.1 and the skin had a shrinking temperature of 161 F. The skin was of a tan .color'and appeared to be well tanned.

Example 5 One dozen pickled domestic sheepskins weighing 20 pounds were drummed for 10 minutes with 20 pounds of a 10% NaCl solution. 0.4 pound of trimethylol melamine (2% of the pickled skins) in the form of a 25% solution was added to the drum and after 15 minutes drumming the liquor had an average pH of 4.3 and the skins were becoming slightly tanned. Another 2% of trimethylol melamine was added and the skins were drummed 15 minutes after which a third feed of 2% trimethylol melamine was added and the drumming continued for 2 hours. At this time the liquor had an average pH of 5.1 and the skins seemed to be well tanned and had a heat resistance of 145 F. 6% of a commercial tanning prepartion containing approximately 50% formaldehyde as the tanning agent was then added to the drum and the skins were drummed for. 2.hours at which time they had a heat resistance of 172 F. 2% of borax was dissolved in warm' water and added to the drum and the skins treated for another hour after which they were taken from the drum,

- horsed up and allowed to dry overnight.

The following day the skins were washed cold for 10 minutes and then washed at F. for 10 minutes, placed in the drum with an approximately equal weight of water at 125 F. and drummed with 12% of a decolorized sulfonated sperm-cocoanut oil mixture. After 45 minutes drumming the fatliquor was not exhausted and 0.5% acetic acid was added. After further drumming for 30 minutes the fatliquor was not 1. A process of preparing leather which comprises impregnating untanned skins with an aqueous dispersion of a methylol melamine and with another tanning agent.

2. A process of preparing leather which comprises impregnating untanned skins with an aqueous dispersion of a methylol melamine and with a vegetable tanning agent.

3. A process of preparing leather which comprises impregnating untanned skins with an aqueous dispersion of a methylol'melamine until the skins are at least partially tanned and thereafter completing the tannage by impregnating the skins with quebracho. extract. 7 r r 4. A process 01 preparing leather which comprises impregnating untanned skins with an aqueous dispersion of a methylol melamine and. with a water-soluble tanning metal salt.

5. A process of preparing leather which comprises impregnating untanned skins with an aqueous dispersion oi a methylol melamine and with a water-soluble chromium salt. Y

6. A process of preparing leather which comprises impregnating untanned skins with an aqueous dispersion of a methylol melamine and with a water-soluble iron salt.

7.' A process of preparing leather which comprises first impregnating untanned skins with an aqueous dispersion of a methylol melamine and then completing the tannage by impregnating the treated skins with another tanning agent. 8. A process of preparing leather which com- 9. A processor preparing leather which comf prises the steps of first impregnating untanned skins with an aqueous dispersion of a methylol melamine and then applying a water-soluble tanning metal salt solution.

10. A process of preparing leather which comprisesthe steps of first impregnating untanned skins with an aqueous dispersion oia methylol melamine and then applyinga water-soluble chromium salt solution. 7

1i. A process of preparing leather which comprises the steps of first impregnatinguntanned skins with an aqueous dispersion of a methylol melamine and then applying a water-soluble iron salt solution. g

12. A process of converting untanned skins into leather which comprises impregnating thev untanned skins with an aqueousdispersion of a.

. water-soluble, water-stable trimethylol melamine in amounts varying from about 1-10%.

by weight based on. the weight oi the untanned skin until the skin is at least partially tanned and thereafter finishing the tanning operation in the presence of another tanning agent.

7 WILLIAM oavm DAWSON. 

